Dynamic Recipient List - 6.3

Talend ESB Mediation Developer Guide

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Design and Development
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Usually one of the main reasons for using the Recipient List pattern is that the list of recipients is dynamic and calculated at runtime. The following example demonstrates how to create a dynamic recipient list using an Expression (which in this case it extracts a named header value dynamically) to calculate the list of endpoints which are either of type Endpoint or are converted to a String and then resolved using the endpoint URIs.

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        errorHandler(deadLetterChannel("mock:error"));

        from("seda:a")
            .recipientList(header("foo"));
    }
};

The above assumes that the header contains a list of endpoint URIs. The following takes a single string header and tokenizes it

from("direct:a").recipientList(
        header("recipientListHeader").tokenize(","));

Iteratable value

The dynamic list of recipients that are defined in the header must be iteratable such as:

  • java.util.Collection

  • java.util.Iterator

  • arrays

  • org.w3c.dom.NodeList

  • a single String with values separated with comma

  • any other type will be regarded as a single value

Using the Spring XML Extensions

<camelContext errorHandlerRef="errorHandler" 
    xmlns="http://camel.apache.org/schema/spring">
    <route>
        <from uri="seda:a"/>
        <recipientList>
            <xpath>$foo</xpath>
        </recipientList>
    </route>
</camelContext>

For further examples of this pattern in use see this JUnit test case.

Using delimiter in Spring XML

In Spring DSL you can set the delimiter attribute for setting a delimiter to be used if the header value is a single String with multiple separated endpoints. By default Camel uses comma as delimiter, but this option lets you specify a customer delimiter to use instead.

<route>
  <from uri="direct:a" />
  <!-- use comma as a delimiter for String based values -->
  <recipientList delimiter=",">
    <header>myHeader</header>
  </recipientList>
</route>

So if myHeader contains a String with the value "activemq:queue:foo, activemq:topic:hello , log:bar" then Camel will split the String using the delimiter given in the XML that was comma, resulting into 3 endpoints to send to. You can use spaces between the endpoints as Camel will trim the value when it lookup the endpoint to send to.

Note: In Java DSL you use the tokenizer to archive the same. The route above in Java DSL:

from("direct:a").recipientList(header("myHeader").tokenize(","));

In Camel 2.1 it is a bit easier as you can pass in the delimiter as second parameter:

from("direct:a").recipientList(header("myHeader"), "#");